Automatic slack adjuster for brakes



Dec. 17, 1940. B. H; BROWALL AUTOMATIC SLACK ADJUSTER FOR BRAKES Filed July l, 1939 3 Sheets--Sheel l 3 Sheets-Sheet 2 Dec. 17, 1940. B. H. BRowALL AUTOMATIC SLACK ADJUSTER FOR BRAKES Filed July 1, 1939 B. H. BRowALL 2,225,001

AUTOMATIC SLACK ADJUSTER FOR BRAKES Patented Dec. 17, 1940 vuru'riazn STATES 2,225,001v AUTOMATIC sLAcx ADJUSTER ron BRAKES Bert Henry Browall, Malmo, Sweden, assignor to Svenska Aktiebolaget Bromsregulator, Malmo, Sweden, a corporation of Sweden I Application July 1, 1939, Serial No. 282,534 In Germany July 2, 1938 14 Claims.

This invention relates to automatic slack adjusters for brakes of the kind comprising a twopart brake rod one part of which is displaceable axially in relation to the other rod part and comprises a screw-threaded spindle, an operating member slidable axially on said other rod part and adapted to be displaced thereon in one direction at application and in the other direction at release of the brake, and axially displaceable nuts on said spindle for coupling said spindle to said other rod part and to said operating member under the control of the movements at application and release of the brake, respec-` tively.

An automatic slack adjuster of this kind is already known, in which the threads of the spindle are of such a pitch as to make them nonselflocking, and in which said nuts are adapted to rotate on the spindle at their axial displacement thereon. In this already known slack adjuster, however, the nuts are rotatable and axially displaceable in one direction only on the spindle, namely in the direction for reducing'excessive slack. For this reason the automatic slack adjuster is single-acting, that is capable only of reducing the slack when too large, and

can not be made double-acting, that is capable not only of reducing the slack when too large but also of increasing the slack when too small.

Further the slack reducing operation of the slack adjuster depends not only on the value of ther slack but also on the elastic deflection of the brake rigging at the continued movement of the brake actuator after it having travelled the distance corresponding to the slack at the application of the brake. The elastic deection of the brake rigging, however, varies with the brake pressure, and for this and other reasons it has been found desirable to make the operation of the slack adjuster independent of the elastic deflection of the brake rigging. For this purpose as well as for the purpose of enabling the slack adjuster to be made double-'acting it is necessary that the nuts are axially displaceable in both directions on the spindle. To this end it has been proposed to make use of non-rotatable nuts split to enable them to be lifted with their threads out of engagement with the threads of the spindle, the nuts being slided with their threads over the threads of the. spindle at the axial displacement of the nuts on the spindle. Obviously in this case the pitch of the threads of the spindle has no special function. The split nuts, however, by their rutchng over the spindle very soon wear out or damage themselves andthe threads of the spindle.

vOne object of the invention is to provide a slack adjuster of the kind set forth inthe opening paragraph herein, in which the nuts are 5 rotatable and axially slidable in relation-to the screw-threaded spindle in both directions in such a manner that the slack reducing operation of the slack adjuster becomes independent of the elastic deection ofthe brake rigging at brak- 10 ing, that the slack adjuster can be made doubleacting if desired, and that the threads of the nut always are in engagement with the threads of the spindle. g l

Another object of the invention is toprovide anautomatic slack adjuster of the character set forth, which works in a reliable. manner and is of a simple construction.

Withfthese and other objectsA in View which will become apparent from the following dey tained description the invention consists in the construction, combination and organization. of parts hereinafter described and illustrated by way of examples on theaccompanying drawings and finaly pointed out inthe appended claims.

In the drawings:

Fig. 1 is an axial section of vone form of the automatic slack adjuster according to the invention. Fig. Zlis a plan-View, Partly in section, illustrating a certain modification of the form of the automatic slack adjuster shown in Fig. 1.

Fig. 3 is a fragmental plan View, partly in section,'illustrating another modification of the same form of the slack adjuster.

Fig. 4 is a fragmental plan view of a conventional vform of brake-rigging and illustrates one manner ofv mounting the automatic slack adjuster therein. p

Fig. 5 is afragmental axial section of another form of the automatic'slack adjuster according to the invention.

Asshown in the drawings the automatic slack adjuster comprisesra two-part brake rod one part of which comprises a screw-spindle I projecting into the tubular other rod part 2 and having screw-threads of such a pitch as to make thescrew-spindle non-selflocking. The screw spindle I has screwed on it a nut 3 for coupling the spindle to the other rod part 2, and a Vsecond nut 4 for coupling the spindle to an operating member 5. The latter is in the shape of a tubular casing which is axially slidable on lthe rod part 2 and houses a coiled compression spring 6 which is inserted between the rod part 2 and 55 the operating member and normally holds the latter pressed with an abutment 20 against an abutment such as a flange I3 carried on the rod part 2. known in the art, is adapted to be displaced axially on the rod part 2 against the action of the spring 6 when at an application of the brake the brake actuator continues its movement after having travelled the distance corresponding to the desired value of the slack. At release of the brake the operating member is returned to its normal position in relation to the rod part 2 by the spring 6. Diiierent .forms of actuating devices for the operating member 5 are known in the art, and according to the example illus `l in the` position corresponding to released brake.

trated in Fig. 4 the operating member 5 is prof vided with an abutment 1 for coaction with an abutment 8 moving in one direction in relation For taking the nut 4 along in the return movev ment of the axially slidable operating member 5 .under the action of the spring 6 at release of the brake the operating member 5 is provided with an abutment 9 for coaction with an abutment ring I5 which is slidable and rotatable on the nut 4 and between which and a collar I 8 on the nut 4 there is inserted a coiled compression spring II. An antifriction thrust bearing I6 is inserted between the ringv I5 and the spring II. The ring I5 forms one part of a slip friction clutch the other part of which is formed by a flange I0 on the nut 4 and is pressed against the iirst named part I 5` by the spring Il. For taking the nut 4 along in the axial displacement of the operating member 5 at the continued movement of the brake actuator, after the latter having travelled the distance corresponding to the desired value of the slack, the operating member 5 is provided with an abutment I 4 coacting with an abutment such as' the collar I8 on the nut 4, and an antifriction thrust bearing I6" is inserted between the abutment I4 and the collar I8 for the easement of the rotation of the nut 4, which enables the nut 4 to be taken along in the said axial displacement. Instead of arranging this antifriction thrust bearing I6" between the abutment I4 and the collar I8, it may be arranged between the spring II and the abutment ring I5 as in the modication illustrated in Fig. 2 wherein an abutment ring I9 is freely rotatable on the nut 4 and is inserted between the two antifriction thrust bearings I6 and I5, the abutment I4 in this modification being arranged for coaction with this ring I9.

As long as the operating member 5 is not displaced with its abutment 20 away from the corresponding abutment I3 on the rod part 2 the nut 3 supports itself in axial direction against the operating member 5 by the intermediary of an antifriction thrust bearing. As shown in Figs. 1, 2 and 5 this bearing may be the same as the antifriction thrust bearing I6' already provided for the nut 4 which is supported against the operating member 5 in the slack increasing ydirection by this bearing I 6 and in turn abuts the nut 3 and holdsthe latter out of contact with the abutment flange I3 on the rod part 2. If it is desired to desist from thus saving one antiiriction bearing in the slack adjuster a sep- The operating member 5, as is well arate antifriction bearing I1 may be arranged for the axial support of the nut 3 against the operating member 5 according to the modification illustrated in Fig. 3. The nut 3 is provided with a flange I2 with which it at commencing movement of the operating member 5 against the action of the spring 6 engages the abutment ange I3 on the rod part 2, the nut 3 being thereby locked against rotation in the slack increasing direction. When rotating and moving axially on the spindle I in the slack reducing direction the nut 3 supports itself axially against the rod part 2 by means of an antifriction thrust bearing I1. In the drawings the slack adjuster is shown At commencing application movement of the brake, as long as the force transmitted from rod part 2 to the spindle I only has to overcome the resistance against movement of the brake rigging, the nut 4 must be held against rotation in ,order to enable the spring 6, the' operating member 5 and the nut 4 to takethe spindle I along in the movement of rod part 2. For this purpose, in the forms of the slack adjuster shown in Figs. 1-3, the power of the spring II must be suflicient for holding the flange I0 in such a irictional engagement lwith the abutment ring I5 as to prevent the flange I0 from slipping in relation to the abutment ring I5 which in turn abuts the abutment 9 and is thereby held against rotation. Should the slack be too small, that is should the brake stress arise inthe brake riggingbefore the operating member 5 is displaced axially by the coacting abutments 1, 8, the spring I I yields under the increasing stress inthe brake rod I, 2, whereby the friction' clutchl I6, I5 is released or enabled to slip under the action oi the torque on the nut 4, which is produced' by the braking stress due to the non-selfloc'king character of the threads of the'spindle I. Consequently, the two nuts 3 and 4 will rotate and move axially on the spindle I in the slack increasing direction. When the brake actuator has travelled the distance corresponding to thev desired value of the slack and when,` at the commencing axial displacement of the operating member 5 against the action of the spring 6, the nut 3 with its abutment ange I2 has engaged the abutment iiange I3 on the operating member 5 the rotation of the nut 3 is stopped, where by the spindle I is coupled to the rod part 2. The brake stress is now transmitted from'the rod part 2 through the abutments I3 and I2 and the nut 3 to the spindle I.

Should the slack be too large, that is should the abutment 8 reach the abutment 1 before the brake stress arises in the brake rigging, the commencing axial displacement of the operating member at the continued movement of the brake actuator results in the nut 3 being locked against rotation by the flange I2 engaging the flange I3, whereby the spindle I is locked to the rod part 2. At the `continued axial displacement of the operating member 5 through the coacting abutments 1 and 8 the operating member 5 through its abutment I4 displaces the nut 4 axially on the spindle I to the left in the figures on the drawings. This displacement of the nut 4 is enabled by rotation of the same, and this rotation takes place easy due to the provision of the antifriction thrust bearing I6". At the displacement of the nut 4 in this direction on the spindle I the friction clutch I0, I5 is inoperative due to the fact that the abutment ring I5 loses its engagement with Jthe abutment ring I is held against rotation. .At the beginning of the brakerelease movement, until'the brake stress has ceased, the spring II will yield a little at the displacement of the operating member 5, so that the friction clutch l0,

-I5 can slip, and vso the nut.4 is displaced under rotation on the spindle I But as soonas the ybrake stress in the brake rigging has ceased the frictionalcontact between the clutch members IIl, I5 will suflice for holding vthe nut 4 against rotation, so that the axial displacement of the operating member 5 in relation to the spindle I ceases and so thatA at the continued brake release movement the operating member 5 and the spindle are displaced in unison in relation to the rod part 2 and 'the nut '3 in the slack reducing direction until the operating member 5 has returned to its normal position. At this `slack reducing movement the nut 3 rotates against its antifriction thrust bearing I'I.

In order to eliminate the necessityof making the spring II which serves the purpose of pressing the parts of the friction clutch III, I5 together and, consequently, also the spring 6 sostrong that the action of these springs under all conditions is sufficient for overcoming lthe resistance against the idle movement of the brake rigging, even if it should be rheavy to move, there may be arranged in addition to the nuts 3 and 4 a third nut 2| on'the spindle I as illustrated in'Fig. 5. This third nut 2| serves the purpose of strengthening the tendency of the spindle I to follow the other rod part 2V at the application of the brake and isprovided, much in the same manner as the nut 4, with a slip friction clutch. One part `25 of this friction clutch is provided on the nut 2|, and the other part 22 consists of an abutment ring 22 with which the nut 2 I, at the application movement of the brake, supports itself against an abutment 26 on the rod part 2, a coiled compression spring 23 which serves the purpose of pressing the parts of the friction clutch 22 and 25 together being inserted between the abutment ringf23 and a collar 21 or the like on the nut 2|. An antifriction thrust bearing 24 is inserted vbetween the spring 23 and any one of its supports,

preferably the abutment ring 22 as shown. The spring 23 can be made so strong that it under all conditions is sucient for overcoming the greatest resistance against the idle movement of the brake rigging, even if it should be heavy to move. Thus it is possible to make the spring II for the nut 4 and, consequently, the spring 6 weaker without running the risk of the slack adjuster performing an unintentional slack increasing vably in the form of l.a one-way clutch spring 33, for positivelyv preventing rotation`r of thering I5 in one directiomnarnelyin the Ydirection ofv slack increasing rotation of the nut 4.

In the forms of the invention herein described for the purpose of illustration the automatic slack adjusted is double-acting, that is capable not only of reducing the slack when'too large but also of increasing the slack when too small. .The capability of the slack adjuster toincrease the slack when too small is due to the nut 3 beingsupported with its iiange I2 out of contact withthe abutment ilange I3 on the rodpart 2 by the operating member 5 through the nut 4, or otherwise,

until at the application of the brake the brake actuator has travelled the distance corresponding to the desired value. of the slack. By desisting from said support ofthe nut 3 during `part ofthe application movement of the'brake, so that the nut 3 engages the abutment I3 during the whole of said movement,the slack adjuster is made single-acting, that is capable zonlyof reducing the slack when too large. Although it is preferable in most cases to make the slack adjuster. doubleacting the inventionis not limited hereto since the essential features of 'the invention are useful and advantageous also inthe case the rslack adjuster ismade single-acting.

What I claim and desire to secure by Letters Patent is:

1. An automatic slack adjuster for brakes,

lcomprising `a two-part brake rod one part of which is displac'eable axially in relation to the other rod part and comprises a screw-threaded the other direction atrelease of the brake, a rs-t nut on said spindle for coupling said spindle to said other rod part at application of the brake, a second nut on said spindle, adapted to be axially displaced on said spindle in both directions by said operating member, an anti-friction thrust bearing for rendering said second'nut easily rotatable at axial displacement in one of said directions, and means including a-slip friction clutch for rendering said second nut-rotatable -at axial displacement in the opposite direction only when acted upon with a certain amount of force.

2. An automatic slack Vadjuster as claimed in claim 1, in which said means forming said slip friction clutch comprises a flange onv said second nut, an axially movable and rotatable abutment member on said nut for coactionY with an `abutment on said operating member, and a kspring acting betweenvsaid abutment member and said second nut for pressing' the latter with its said flange in frictional contact with said abutmenty member and for mediatingthe axial support of said second nut against said operating member at the axial displacement thereof at release of the brake.

3. An automatic slack adjuster as` claimed in claim 1, in which an antifriction thrust bearing is provided for rendering saidrst nut easily rotatable and for axially supporting the same against said operating member in 'a position out of contact with an abutment on said other rod 4part until at application of the .brake the axial displacement of said operating member inr relation to said other rod part commences, said nrs-t nut being permitted by such commencing movement of said operating member-to. abut said abuti ment onY said other rod part 'and therebyft'o lock itself 'against-movement in slack increasing direction in relation to said spindle.

4. An automatic slack adjuster as claimed in claim 1, which includes a third nut on said spindle, means forming a slip friction clutch between said third nut and said other rod part for axially supporting saidv third nut against said other rod part in one direction, and an antifriction thrust .bearing for axially' supporting said third nut against said other rod part in the other direction.

5. An automatic slack adjuster for brakes, comprising a two-part brake rod one part of which is displaceable axially in relation to the other rod par-t and comprises a screw-threaded spindle the threads of which are of such a pitch as to render them lnon-selfl'ocking, an operating member movable axially on said brake rod and adapted to be moved axially in relation to said other rod part in one direction at application and in the other direction at release of the brake, a rst nut screwed on said spindle for coupling said spindle to said other rod part, a second nut screwed on'said spindle, two antifriction thrust bearings interposed between said operating member and said second nut for transmitting' the axial movements of said operating member in one direction and the other, respectively, to said second nut, and means for producing a slip frictional resistance against rotation of said second nut at axial displacement thereof by the axial movement of said operating member at release of the brake 6. An automatic slack adjuster for brakes, comprising a two-part brake rod one part of which is displaceable axially in relation to the tubular other rod part and comprises a screwthreaded spindle the threads of which are of such a pitch as to make them non-selflocking, `an 4operating member in Ithe shape of a tubular casing slidable axially on said brake rod and adapted to be displaced axially in relation to said other rod part in one direc-tion at application and in the other direction at release of the brake, a first nut screwed on said spindle for coupling said spindle to said other rod part at application of the brake, a second nut screwed on said spindle for coupling said spindle to said operating member at release of the brake, means including an antifriction thrust bearing for rendering said second nut easily rotatable and for axially supporting the same against said operating member at the axial displacement thereof at application `of the brake, a spring carried on said second nut for yieldingly supporting said second nut axially against said operating member at vthe axial dis'- placement thereof at release of the brake, an abutment member axially movable and rotatable on said second nut and interposed between said spring and said operating member for coaction with an abutment thereon, and a flange on said second nut, with which said second nut is pressed axially by said spring against said abutment member for slip frictionally coupling said second nut to said abutment member.

7. An automatic slack adjuster as claimed in claim 6, which includes a third nut on said spindle for aiding in coupling said spindle to said other rod part, a spring carried on said third nut for yieldingly supporting said third nut axially in one direction against said other rod part, an abutment member axially movable and rotatable on said third nut and interposed between said spring on said third nut and said other rod part kforfcoactior'i with an abutment thereon, and a flange on said third nut,l withwhich said third nut by said spring thereon is pressed axially against said movable abutment member on said third nut, said springon said third. nut being stronger than said spring on said second nut.

8. 'An automatic slack adjuster as claimed in claimk 6, in which said spring supports itself at one vend against said abutment member on said second nut by the intermediary of an antifriction thrust bearing, and' in which said second nut, until at application ofthe brake the axial displacement of said operating member in relation to said otherrod vpart commences, abuts said first nut and thereby holds the latter in a position out of contact with an abutment on said other rod part, with which -said rst nut is permitted to makel Contact and thereby to lock itself against rotation at the commencement of the said axial displacement of said operating member at the application of the brake.

9. An automatic `'slack adjuster as claimed in claim I1, in which there is provided a one-way locking deviceconnecting said slip 'friction clutch to said operating member and acting against rotation in theV slack increasing direction.

10. An automatic slack adjuster as claimed in claim 1, in which said second nut is adapted to axially support said rst nut in a position out of contact with an abutment on said other rod part until, at application of the brake, the axial displacement of said operating member and said second nut in relation to said other rod part commences, said iirst nut being'permitted by such commencing movement of said operating member and'said'second nut to abut said abutment on saidY other rod part and thereby to lock itself against movement in slack increasing direction in relation 'to said spindle.

v 11. An automatic slack adjuster as claimed in claim 6, in which there are provided on said second nut a second axially movable and rotatable abutment member adapted for coaction with an abutment on said operating member for taking said second nut along in the axial displacement of said operating member at application of the brake, said antifriction thrust bearing being inserted between said labutment members, and a second antifriction thrust bearing inserted between said spring and said second abutment member.

12. An automatic slack adjuster as claimed in claim 6, -in which said second nut, until at application of the 'brake the axial displacement of said operating member in relation to said other rod part commences, Yabuts said first nut and thereby holds the latter out of contact with an abutment for the same on said other rod part, and in which there are provided on said second nut a second axially movable androtatable abutment member adapted for coaction with an abutment on said operating member for taking said second nut along in the axial displacement of said operating member at application of the brake, saidantifriction thrust bearing being inserted between 'said abutment members, and a second antifriction thrust bearing inserted between said spring and said second abutment member.

13. An automatic slack adjuster as claimed in claim 6, in which there is provided a one-way locking device connecting said abutment member to said operating member for positively preventing rotation of said abutment member in the direction of slack increasing rotation of said second nut.

14. An automatic slack adjuster for brakes, comprising a two-part brake rod one part of which is displaceable axially in relation to the other rod part and comprises a screw-threaded spindle the threads of which are of such a 'pitch as to render them non-selflocking, an operating member movable axially on said brake rod and adapted to be moved axially in relation to said other rod part in one direction at application and in the other direction at release of the brake, a rst nut screwed on said spindle, an antifriction thrust bearing interposed between said rst nut and said other rod part to facilitate rotation of said first nut in one direction, coacting seats on said rst nut and said other rod part to prevent rotation of said first nut in the other direction and thus coupling said spindle to said other rod part, a 4 second nut screwed on said spindle, two antifriction thrust bearings interposed between said operating member and said second nut for transmitting the axial movements of said operating member in one direction and the other', respectively, to said second nut, coacting abutment surfaces on said rst and second nuts to keep said seat on said first nut out of engagement with the corresponding seat on said other rod part as long as said second nut and said operating member take a position in relation to each other cor-v responding to released brake, and means for producing a slip frictional resistance against rotation of said second nut at axial displacement thereof by the axial movement of said operating member at release of the brake.

. BERT HENRY BROWALL. 

